Problem: Simplify the following expression: $y = \dfrac{k^2 - 3k - 18}{k - 6} $
Explanation: First factor the polynomial in the numerator. $ k^2 - 3k - 18 = (k - 6)(k + 3) $ So we can rewrite the expression as: $y = \dfrac{(k - 6)(k + 3)}{k - 6} $ We can divide the numerator and denominator by $(k - 6)$ on condition that $k \neq 6$ Therefore $y = k + 3; k \neq 6$